Conventionally, as a device of this type, for example, a power supply device for a slide seat described in Patent Document 1 is known. This power supply device is configured by including a case having a harness accommodation portion, a movable body that advances or retreats along the case, and a wire harness that bends within the harness accommodation portion while one end portion of the wire harness being supported by the movable body and the other end portion of the wire harness being supported by the case. Further, the wire harness is distributed along the movable body to be connected to a circuit on the side of a slide seat, and a circuit on the side of a power supply of a vehicle is connected to a connector of the case. Thus, the movable body advances or retreats simultaneously with advancing or retreating of the slide seat, and electric power is supplied from the circuit on the side of the power supply of the vehicle to the circuit on the side of the slide seat via the wire harness.